Hi @Apurva D ,
As per as my research, the official documentation does not mention how does the "lastfullbackup" date gets updated or what triggers it be up-to-date.
It may have something to do with transaction log file updates. Please refer to: Full backups
Also, there is an article that describes how to use a script to check when a mailbox database was last backed up on an Exchange server. Hope it can help: PowerShell Script: Check Exchange Mailbox Database Last Backup Time
Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.
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